1. Field of the Invention
The present invention relates to a brushless motor incorporated in a pump, and more particularly to a brushless motor control apparatus for a pump for controlling a brushless motor.
2. Description of Related Art
As a technique of this kind, a brushless motor control apparatus described, for example, in U.S. Pat. No. 2,642,357 has been known. The brushless motor described in the patent publication detects a phase based on a neutral point of induced voltage in each phase coil. There are cases in which, as an induced voltage changes, a pulse-shaped back voltage is generated possibly resulting in erroneous detection of a phase. To prevent such erroneous detection of a phase, the control apparatus described in U.S. Pat. No. 2,642,357 applies a mask to neutral point detection for a certain amount of time.
It is stated, for example, in Japanese unexamined patent publication No. 2003-88080 that, in recent years, a brushless motor is adopted for a pump so as to miniaturize the pump.
In this regard, however, the control described in U.S. Pat. No. 2,642,357 is not necessarily applicable to every type of brushless motor. Namely, in the case of a brushless motor with large inductance, a brushless motor which draws a large current or a brushless motor for use in a low-revolution range, a pulse-shaped induced voltage stays relatively long, so that it becomes necessary to change the amount of time during which a mask is applied to neutral point detection depending on the type of the brushless motor. Hence, it is not possible to commonly use a same control circuit to control different types of brushless motors.